The purpose of using nematophagous fungi as biological control agents of gastrointestinal nematodes of livestock is to reduce the build-up of infective larvae on pasture and thus avoid clinical and subclinical disease. As the interaction of fungus-larval stages takes place in the environment, it is crucial to know how useful the fungal agents are throughout the seasons in areas where livestock graze all year-round. This study was designed to determine the predatory ability of the nematophagous fungus Duddingtonia flagrans against gastrointestinal nematodes of cattle during four experiments set up in different seasons. In each experiment, faeces containing eggs of gastrointestinal nematodes were mixed with 11,000 chlamydospores/g and deposited on pasture plots. A comparison between fungal-added faeces and control faeces without fungus were made with regard to pasture infectivity, larval presence in faecal pats, faecal cultures, faecal pat weight, and temperature inside the faecal mass. In three of the four experiments, Duddingtonia flagrans significantly reduced the population of infective larvae in cultures (68 to 97%), on herbage (80 to 100%), and inside the faecal pats (70 to 95%). The study demonstrated the possibility of counting on a biological control tool throughout most of the year in cattle regions with extensive grazing seasons.

The oral application of chlamydospores of the nematophagous fungus Duddingtonia flagrans allows reducing the number of infective larvae (L3) in faeces and decreases the infectivity of the pastures of gastrointestinal nematodes. There are differences in the literature about the quantity of chlamydospores required for the reduction of L3 and there is little data about the importance of the concentration of parasite eggs in faeces in relation to the predatory effect of fungus. This study evaluated the reduction of L3 in faeces taking into account four concentrations of chlamydospores of D. flagrans with four concentrations of faecal eggs per gram (epg). Two hundred coprocultures were performed with 10 g each one, using faeces from four parasitised sheep with natural infections. The coprocultures were distributed in treated groups (GT) containing 180, 620, 1460 and 3600 epg along with 1000, 6250, 3000 and 11,000 chlamydospores per gram of faeces. Four control groups without chlamydospores were performed for each GT. The coprocultures were incubated for 16 days at room temperature of 27°C. The reduction percentages for the group of 11,000 chlamydospores and epg 180, 620, 1460 and 3600 were 6.51%; 1.35%; 52% and 85%, respectively. In the group of 6250 chlamydospores the reduction percentages for epg 180, 620, 1460 and 3600 were 16%; 20%; 66% and 67%, respectively. These results would indicate that the predatory capacity of D. flagrans can be dependent on the stimulus generated by the presence of larvae as well as the concentration of chlamydospores present in the faeces.

Nematophagous fungi are a biological control tool used against gastrointestinal nematodes in livestock. These fungi prey on free-living larvae in faeces and could be affected by active drugs excreted post-treatment. This study aimed to determine in vitro and under environmental conditions the effect of the following anthelmintics on the fungus Duddingtonia flagrans: ivermectin, levamisole, albendazole, fenbendazole and ricobendazole. The in vitro effect of anthelmintics on fungal growth and predatory capacity was assessed in corn meal agar and coprocultures, respectively. Ivermectin (1, 2 and 10 ppm), fenbendazole (0.027, 0.054 and 1 ppm) and albendazole (1 ppm) significantly affected fungal development. The fungal efficacy against L3 was high in the control and levamisole coprocultures but decreased significantly in the presence of albendazole, fenbendazole, ricobendazole and ivermectin. The impact of levamisole on D. flagrans was further assessed under environmental conditions in autumn and winter; the fungal efficacy measured in faecal pats and the surrounding herbage was not affected by levamisole at any time. This study shows that using albendazole, fenbendazole, ricobendazole or ivermectin may compromise fungal activity, as these drugs affect the free-living stages of nematodes in faeces, but levamisole can be safely considered in parasite control strategies involving D. flagrans and anthelmintic treatments.